Intercooled cooling air with auxiliary compressor control

ABSTRACT

A gas turbine engine includes a main compressor section with a downstream most location. A turbine section has a high pressure turbine. A tap line is connected to tap air from a location upstream of the downstream most location in the main compressor section. The tapped air is connected to a heat exchanger and then to a cooling compressor. The cooling compressor compresses air downstream of the heat exchanger, and is connected to deliver air into the high pressure turbine. A bypass valve is positioned downstream of the main compressor section, and upstream of the heat exchanger. The bypass valve selectively delivers air directly to the cooling compressor without passing through the heat exchanger under certain conditions.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/967,446 filed Dec. 14, 2015.

BACKGROUND

This application relates to improvements in providing cooling air from acompressor section to a turbine section in a gas turbine engine.

Gas turbine engines are known and typically include a fan delivering airinto a bypass duct as propulsion air. Further, the fan delivers air intoa compressor section where it is compressed. The compressed air passesinto a combustion section where it is mixed with fuel and ignited.Products of this combustion pass downstream over turbine rotors drivingthem to rotate.

It is known to provide cooling air from the compressor to the turbinesection to lower the operating temperatures in the turbine section andimprove overall engine operation. Typically, air from the highcompressor discharge has been tapped, passed through a heat exchanger,which may sit in the bypass duct and then delivered into the turbinesection. The air from the downstream most end of the compressor sectionis at elevated temperatures.

SUMMARY

In a featured embodiment, a gas turbine engine includes a maincompressor section with a downstream most location. A turbine sectionhas a high pressure turbine. A tap line connects to tap air from alocation upstream of the downstream most location in the main compressorsection. The tapped air connects to a heat exchanger and then to acooling compressor. The cooling compressor compresses air downstream ofthe heat exchanger, and connects to deliver air into the high pressureturbine. A bypass valve is positioned downstream of the main compressorsection, and upstream of the heat exchanger. The bypass valveselectively delivers air directly to the cooling compressor withoutpassing through the heat exchanger under certain conditions.

In another embodiment according to the previous embodiment, the bypassvalve is positioned on the tap line, and a separate bypass line connectsthe tap line to the cooling compressor without passing through the heatexchanger.

In another embodiment according to any of the previous embodiments, thebypass valve completely bypasses the heat exchanger.

In another embodiment according to any of the previous embodiments, thebypass valve may be modulated to control the volume of air deliveredthrough the heat exchanger.

In another embodiment according to any of the previous embodiments, thebypass valve completely bypasses the heat exchanger.

In another embodiment according to any of the previous embodiments, thebypass valve may be modulated to control the volume of air deliveredthrough the heat exchanger.

In another embodiment according to any of the previous embodiments, thebypass valve is positioned by a control to bypass the heat exchanger atrelatively low power conditions, including idle.

In another embodiment according to any of the previous embodiments, thebypass valve is positioned by the control to flow all air through theheat exchanger under higher power conditions, including take-off.

In another embodiment according to any of the previous embodiments, thecooling compressor includes a centrifugal compressor impeller.

In another embodiment according to any of the previous embodiments, airtemperatures at a downstream-most location of the high pressurecompressor are greater than or equal to 1350° F. (732° C.).

In another embodiment according to any of the previous embodiments, theturbine section drives a bull gear, the bull gear further driving animpeller of the cooling compressor.

In another embodiment according to any of the previous embodiments, thebull gear also drives an accessory gearbox.

In another embodiment according to any of the previous embodiments, thecooling compressor includes a centrifugal compressor impeller.

In another embodiment according to any of the previous embodiments, airtemperatures at a downstream-most location of the high pressurecompressor are greater than or equal to 1350° F. (732° C.).

In another embodiment according to any of the previous embodiments, airtemperatures at a downstream-most location of the high pressurecompressor are greater than or equal to 1350° F. (732° C.).

In another embodiment according to any of the previous embodiments, theturbine section drives a bull gear, the bull gear further driving animpeller of the cooling compressor.

In another embodiment according to any of the previous embodiments, thebull gear also drives an accessory gearbox.

In another featured embodiment, a gas turbine engine includes a maincompressor section with a downstream most location. A turbine sectionhas a high pressure turbine. There is a means to tap air from a locationupstream of the downstream most location in the main compressor section.The means cools the tapped air and then compresses the air, anddelivering air into the high pressure turbine. There is a means forselectively delivering the tapped air directly to be compressed withoutbeing cooled under certain conditions.

In another embodiment according to the previous embodiment, the means totap includes a heat exchanger and a cooling compressor.

In another embodiment according to any of the previous embodiments, themeans for selectively delivering the tapped air includes a bypass valve,a bypass line and a control for the bypass valve.

These and other features may be best understood from the followingdrawings and specification.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically shows an embodiment of a gas turbine engine.

FIG. 2 shows a prior art engine.

FIG. 3 shows one example engine.

FIG. 4 is a graph illustrating increasing temperatures of a tapped airagainst the work required.

FIG. 5 shows a detail of an example of an engine.

FIG. 6 shows a further detail of the example engine of FIG. 5.

FIG. 7 shows an additional feature.

FIG. 8 shows the FIG. 7 system in a distinct position.

DETAILED DESCRIPTION

FIG. 1 schematically illustrates an example gas turbine engine 20 thatincludes a fan section 22, a compressor section 24, a combustor section26 and a turbine section 28. Alternative engines might include anaugmenter section (not shown) among other systems or features. The fansection 22 drives air along a bypass flow path B while the compressorsection 24 draws air in along a core flow path C where air is compressedand communicated to a combustor section 26. In the combustor section 26,air is mixed with fuel and ignited to generate a high pressure exhaustgas stream that expands through the turbine section 28 where energy isextracted and utilized to drive the fan section 22 and the compressorsection 24.

Although the disclosed non-limiting embodiment depicts a turbofan gasturbine engine, it should be understood that the concepts describedherein are not limited to use with turbofans as the teachings may beapplied to other types of turbine engines; for example a turbine engineincluding a three-spool architecture in which three spoolsconcentrically rotate about a common axis and where a low spool enablesa low pressure turbine to drive a fan via a gearbox, an intermediatespool that enables an intermediate pressure turbine to drive a firstcompressor of the compressor section, and a high spool that enables ahigh pressure turbine to drive a high pressure compressor of thecompressor section.

The example engine 20 generally includes a low speed spool 30 and a highspeed spool 32 mounted for rotation about an engine central longitudinalaxis A relative to an engine static structure 36 via several bearingsystems 38. It should be understood that various bearing systems 38 atvarious locations may alternatively or additionally be provided.

The low speed spool 30 generally includes an inner shaft 40 thatconnects a fan 42 and a low pressure (or first) compressor section 44 toa low pressure (or first) turbine section 46. The inner shaft 40 drivesthe fan 42 through a speed change device, such as a geared architecture48, to drive the fan 42 at a lower speed than the low speed spool 30.The high-speed spool 32 includes an outer shaft 50 that interconnects ahigh pressure (or second) compressor section 52 and a high pressure (orsecond) turbine section 54. The inner shaft 40 and the outer shaft 50are concentric and rotate via the bearing systems 38 about the enginecentral longitudinal axis A.

A combustor 56 is arranged between the high pressure compressor 52 andthe high pressure turbine 54. In one example, the high pressure turbine54 includes at least two stages to provide a double stage high pressureturbine 54. In another example, the high pressure turbine 54 includesonly a single stage. As used herein, a “high pressure” compressor orturbine experiences a higher pressure than a corresponding “lowpressure” compressor or turbine.

The example low pressure turbine 46 has a pressure ratio that is greaterthan about 5. The pressure ratio of the example low pressure turbine 46is measured prior to an inlet of the low pressure turbine 46 as relatedto the pressure measured at the outlet of the low pressure turbine 46prior to an exhaust nozzle.

A mid-turbine frame 58 of the engine static structure 36 is arrangedgenerally between the high pressure turbine 54 and the low pressureturbine 46. The mid-turbine frame 58 further supports bearing systems 38in the turbine section 28 as well as setting airflow entering the lowpressure turbine 46.

Airflow through the core airflow path C is compressed by the lowpressure compressor 44 then by the high pressure compressor 52 mixedwith fuel and ignited in the combustor 56 to produce high speed exhaustgases that are then expanded through the high pressure turbine 54 andlow pressure turbine 46. The mid-turbine frame 58 includes vanes 60,which are in the core airflow path and function as an inlet guide vanefor the low pressure turbine 46. Utilizing the vane 60 of themid-turbine frame 58 as the inlet guide vane for low pressure turbine 46decreases the length of the low pressure turbine 46 without increasingthe axial length of the mid-turbine frame 58. Reducing or eliminatingthe number of vanes in the low pressure turbine 46 shortens the axiallength of the turbine section 28. Thus, the compactness of the gasturbine engine 20 is increased and a higher power density may beachieved.

The disclosed gas turbine engine 20 in one example is a high-bypassgeared aircraft engine. In a further example, the gas turbine engine 20includes a bypass ratio greater than about six (6), with an exampleembodiment being greater than about ten (10). The example gearedarchitecture 48 is an epicyclical gear train, such as a planetary gearsystem, star gear system or other known gear system, with a gearreduction ratio of greater than about 2.3.

In one disclosed embodiment, the gas turbine engine 20 includes a bypassratio greater than about ten (10:1) and the fan diameter issignificantly larger than an outer diameter of the low pressurecompressor 44. It should be understood, however, that the aboveparameters are only exemplary of one embodiment of a gas turbine engineincluding a geared architecture and that the present disclosure isapplicable to other gas turbine engines.

A significant amount of thrust is provided by the bypass flow B due tothe high bypass ratio. The fan section 22 of the engine 20 is designedfor a particular flight condition—typically cruise at about 0.8 Mach andabout 35,000 feet. The flight condition of 0.8 Mach and 35,000 ft., withthe engine at its best fuel consumption—also known as “bucket cruiseThrust Specific Fuel Consumption (‘TSFC’)”—is the industry standardparameter of pound-mass (lbm) of fuel per hour being burned divided bypound-force (lbf) of thrust the engine produces at that minimum point.

“Low fan pressure ratio” is the pressure ratio across the fan bladealone, without a Fan Exit Guide Vane (“FEGV”) system. The low fanpressure ratio as disclosed herein according to one non-limitingembodiment is less than about 1.50. In another non-limiting embodimentthe low fan pressure ratio is less than about 1.45.

“Low corrected fan tip speed” is the actual fan tip speed in ft/secdivided by an industry standard temperature correction of [(Tram °R)/(518.7° R)]^(0.5). The “Low corrected fan tip speed”, as disclosedherein according to one non-limiting embodiment, is less than about 1150ft/second.

The example gas turbine engine includes the fan 42 that comprises in onenon-limiting embodiment less than about 26 fan blades. In anothernon-limiting embodiment, the fan section 22 includes less than about 20fan blades. Moreover, in one disclosed embodiment the low pressureturbine 46 includes no more than about 6 turbine rotors schematicallyindicated at 34. In another non-limiting example embodiment the lowpressure turbine 46 includes about 3 turbine rotors. A ratio between thenumber of fan blades 42 and the number of low pressure turbine rotors isbetween about 3.3 and about 8.6. The example low pressure turbine 46provides the driving power to rotate the fan section 22 and thereforethe relationship between the number of turbine rotors 34 in the lowpressure turbine 46 and the number of blades 42 in the fan section 22disclose an example gas turbine engine 20 with increased power transferefficiency.

Gas turbine engines designs are seeking to increase overall efficiencyby generating higher overall pressure ratios. By achieving higheroverall pressure ratios, increased levels of performance and efficiencymay be achieved. However, challenges are raised in that the parts andcomponents associated with a high pressure turbine require additionalcooling air as the overall pressure ratio increases.

The example engine 20 utilizes air bleed 80 from an upstream portion ofthe compressor section 24 for use in cooling portions of the turbinesection 28. The air bleed is from a location upstream of the discharge82 of the compressor section 24. The bleed air passes through a heatexchanger 84 to further cool the cooling air provided to the turbinesection 28. The air passing through heat exchanger 84 is cooled by thebypass air B. That is, heat exchanger 84 is positioned in the path ofbypass air B.

A prior art approach to providing cooling air is illustrated in FIG. 2.An engine 90 incorporates a high pressure compressor 92 downstream ofthe low pressure compressor 94. As known, a fan 96 delivers air into abypass duct 98 and into the low pressure compressor 94. A downstreammost point, or discharge 82 of the high pressure compressor 92 providesbleed air into a heat exchanger 93. The heat exchanger is in the path ofthe bypass air in bypass duct 98, and is cooled. This high pressure hightemperature air from location 82 is delivered into a high pressureturbine 102.

The downstream most point 82 of the high pressure compressor 82 is knownas station 3. The temperature T3 and pressure P3 are both very high.

In future engines, T3 levels are expected to approach greater than orequal to 1350° F. (732° C.). Current heat exchanger technology isbecoming a limiting factor as they are made of materials, manufacturing,and design capability which have difficulty receiving such hightemperature and pressure levels.

FIG. 3 shows an engine 100 coming within the scope of this disclosure. Afan 104 may deliver air B into a bypass duct 105 and into a low pressurecompressor 106. High pressure compressor 108 is positioned downstream ofthe low pressure compressor 106. A bleed 110 taps air from a locationupstream of the downstream most end 82 of the high pressure compressor108. This air is at temperatures and pressures which are much lower thanT3/P3. The air tapped at 110 passes through a heat exchanger 112 whichsits in the bypass duct 105 receiving air B. Further, the air from theheat exchanger 112 passes through a compressor 114, and then into aconduit 115 leading to a high turbine 117. This structure is all shownschematically.

Since the air tapped at point 110 is at much lower pressures andtemperatures than the FIG. 2 prior art, currently available heatexchanger materials and technology may be utilized. This air is thencompressed by compressor 114 to a higher pressure level such that itwill be able to flow into the high pressure turbine 117.

An auxiliary fan 116 may be positioned upstream of the heat exchanger112 as illustrated. The main fan 104 may not provide sufficient pressureto drive sufficient air across the heat exchanger 112. The auxiliary fanwill ensure there is adequate air flow in the circumferential locationof the heat exchanger 112.

In one embodiment, the auxiliary fan may be variable speed, with thespeed of the fan varied to control the temperature of the air downstreamof the heat exchanger 112. As an example, the speed of the auxiliary fanmay be varied based upon the operating power of the overall engine.

Referring to FIG. 4, a temperature/entropy diagram illustrates that alower level of energy is spent to compress air of a lower temperature tothe desired P3 pressure level. Cooler air requires less work to compresswhen compared to warmer air. Accordingly, the work required to raise thepressure of the air drawn from an early stage of the compressor sectionis less than if the air were compressed to the desired pressure withinthe compressor section. Therefore, high pressure air at P3 levels orhigher can be obtained at significantly lower temperatures than T3. Asshown in FIG. 4, to reach a particular pressure ratio, 50 for example,the prior system would move from point 2 to point 3, with a dramaticincrease in temperature. However, the disclosed or new system moves frompoint 2 to point 5 through the heat exchanger, and the coolingcompressor then compresses the air up to point 6. As can be appreciated,point 6 is at a much lower temperature.

FIG. 5 shows a detail of compressor 114 having an outlet into conduit115. A primary tower shaft 120 drives an accessory gearbox 121. Theshaft 126 drives a compressor rotor within the compressor 114. Theshafts 120 and 126 may be driven by a bull gear 125 through respectivegears 124 and 126. The bull gear 125 is driven by a turbine rotor, andin one example, with a high pressure compressor rotor.

FIG. 6 shows an example wherein a gear 128 is driven by the shaft 126to, in turn, drive a gear 130 which drives a compressor impeller 129. Aninput 132 to the compressor impeller 129 supplies the air from the tap110. The air is compressed and delivered into the outlet conduit 115.

By providing a gear ratio multiplier between the compressor impeller 129and the high spool bull gear 125, the compressor impeller may be drivento operate an optimum speed. As an example, the gear ratio increase maybe in a range of 5:1-8:1, and in one embodiment, 6:1.

Details of the engine, as set forth above, may be found in co-pendingU.S. patent application Ser. No. 14/695,578, which is incorporatedherein by reference in its entirety.

With the system of FIGS. 1-6, all of the air will be cooled, and thus atlow power settings, the turbine disk may be cooler than would bedesirable.

FIG. 7 shows an embodiment 150 that can be incorporated into any of theforegoing embodiments. In the FIG. 7 embodiment 150, the air is tappedfrom the low pressure compressor 152, and passed through a heatexchanger 154 from a tap 156, again as in the prior embodiment. A higherpressure compressor 153 may also have the tap at an upstream location. Abypass valve 158 is positioned intermediate the compressor 152 and theheat exchanger 154. The bypass valve 158 selectively bypasses air into apassage 160 leading directly to the cooling compressor 162, and line 164heading to the high pressure turbine, without passing through the heatexchanger 154. In embodiments, the bypass valve 158 may be capable ofcompletely bypassing all air flow around the heat exchanger 154. Inanother embodiment, it may be able to modulate the bypassed volume.

In the embodiment 150, and as shown in FIG. 8, at low power settings,the bypass valve 158 may be opened. A control 159 is shown schematicallycontrolling the bypass valve 158. The control 159 may open the bypassvalve to deliver air through line 160, and not pass into heat exchanger154 at low power settings, such as idle or cruise.

On the other hand, at higher power settings, such as take-off and climb,the valve 158 may be positioned in the FIG. 7 position at which the airpasses through the heat exchanger 154 for cooling.

A gas turbine engine under this disclosure could be said to include amain compressor section with a downstream most location. A turbinesection has a high pressure turbine. There is a means to tap air from alocation upstream of the downstream most location in the main compressorsection. The means cools the tapped air, then compresses the air, anddelivers air into the high pressure turbine. There is a means forselectively delivering the tapped air directly to be compressed withoutbeing cooled under certain conditions.

The means to tap includes a heat exchanger and a cooling compressor.

The means for selectively delivering the tapped air includes a bypassvalve, a bypass line and a control for the bypass valve.

Although an example embodiment has been disclosed, a worker of ordinaryskill in this art would recognize that certain modifications would comewithin the scope of this disclosure. For that reason, the followingclaims should be studied to determine the scope and content of thisdisclosure.

What is claimed is:
 1. A gas turbine engine comprising; a fan fordelivering air into a bypass duct and into main compressor section witha downstream most location; a turbine section having a high pressureturbine; a tap line configured to tap air from a location upstream ofsaid downstream most location in said main compressor section, said tapline connected to a heat exchanger and then to a cooling compressor,said cooling compressor configured to compress air downstream of saidheat exchanger, and connected to deliver air into said high pressureturbine; a bypass valve positioned downstream of said main compressorsection, and upstream of said heat exchanger, wherein said bypass valveis configured to selectively deliver air directly to said coolingcompressor without passing through said heat exchanger under certainconditions; and wherein said heat exchanger is cooled by air; andwherein said turbine section drives a bull gear, said bull gear furtherdriving an impeller of said cooling compressor.
 2. The gas turbineengine as set forth in claim 1, wherein said bypass valve is positionedon said tap line, and a separate bypass line connecting said tap line tosaid cooling compressor without passing through said heat exchanger. 3.The gas turbine engine as set forth in claim 1, wherein said bypassvalve completely bypasses said heat exchanger.
 4. The gas turbine engineas set forth in claim 1, wherein said bypass valve can be modulated tocontrol the volume of air delivered through the heat exchanger.
 5. Thegas turbine engine as set forth in claim 1, wherein said bypass valve ispositioned by a control to bypass the heat exchanger at relatively lowpower conditions, including idle.
 6. The gas turbine engine as set forthin claim 5, wherein said bypass valve is positioned by said control toflow all air through the heat exchanger under higher power conditions,including take-off.
 7. The gas turbine engine as set forth in claim 6,wherein said cooling compressor includes a centrifugal compressorimpeller.
 8. The gas turbine engine as set forth in claim 1, whereinsaid cooling compressor includes a centrifugal compressor impeller. 9.The gas turbine engine as set forth in claim 8, wherein air temperaturesat the downstream most location of said high pressure compressor aregreater than or equal to 1350° F. (732° C.).
 10. The gas turbine engineas set forth in claim 1, wherein air temperatures at the downstream mostlocation of said high pressure compressor are greater than or equal to1350° F. (732° C.).
 11. The gas turbine engine as set forth in claim 1,wherein said bull gear also drives an accessory gearbox.
 12. The gasturbine engine as set forth in claim 1, wherein said heat exchanger ispositioned within said bypass duct, and air delivered by said fan intosaid bypass duct cools aft from said tap line.
 13. The gas turbineengine as set forth in claim 1, wherein said turbine section has a fandrive turbine driving said fan through a gear reduction.
 14. A gasturbine engine comprising: a fan for delivering air into a bypass ductand into main compressor section with a downstream most location; aturbine section having a high pressure turbine; a tap line configured totap air from a location upstream of said downstream most location insaid main compressor section, said tap line connected to a heatexchanger and then to a cooling compressor, said cooling compressorconfigured to compress air downstream of said heat exchanger, andconnected to deliver air into said high pressure turbine; a bypass valvepositioned downstream of said main compressor section, and upstream ofsaid heat exchanger, wherein said bypass valve is configured toselectively deliver air directly to said cooling compressor withoutpassing through said heat exchanger under certain conditions; whereinsaid heat exchanger is cooled by air; wherein said bypass valve ispositioned by a control to bypass the heat exchanger at relatively lowpower conditions, including idle wherein said bypass valve is positionedby said control to flow all air through the heat exchanger under higherpower conditions, including take-off; wherein said cooling compressorincludes a centrifugal compressor impeller; wherein air temperatures atthe downstream most location of said high pressure compressor aregreater than or equal to 1350° F. (732° C.); and wherein said turbinesection drives a bull gear, said bull gear further driving of saidcooling compressor impeller.
 15. The gas turbine engine as set forth inclaim 14, wherein said bull gear also drives an accessory gearbox.
 16. Agas turbine engine comprising; a fan for delivering air into a bypassduct and into a main compressor section with a downstream most location;a turbine section having a high pressure turbine; a tap line configuredto tap air from a location upstream of said downstream most location insaid main compressor section, said tap line connected to a heatexchanger and then to a cooling compressor, said cooling compressorconfigured to compress air downstream of said heat exchanger, andconnected to deliver air into said high pressure turbine; and a bypassvalve positioned downstream of said main compressor section, andupstream of said heat exchanger, wherein said bypass valve is configuredto selectively deliver air directly to said cooling compressor withoutpassing through said heat exchanger under certain conditions; and saidcooling compressor being driven by a tower shaft driven by said turbinesection.
 17. The gas turbine engine as set forth in claim 16, whereinsaid tower shaft drives a bull gear, said bull gear further driving saidcooling compressor.
 18. The gas turbine engine as set forth in claim 17,wherein said bull gear also drives an accessory gearbox.